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Guru of Grounding
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re: Why Use a Better DAC?
Guru of Grounding   12/10/2008 6:35:38 PM
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The author has confused the issue of differing level standards between professional and consumer audio equipment. First, the NOMINAL or "reference level" signals are +4 dBu (1.23 volts rms) in pro gear and -10 dBV (0.316 volts rms) in consumer gear. The 2.0 volt rms or 5.6 volt pk-pk number for consumer gear refers to a FULL-SCALE rating. This level is only 16 dB higher than the consumer reference by the way, not 22 dB. Therefore, a consumer output is still legitimately rated at -10 dBV reference level but will clip at an output level 16 dB higher - this is referred to as "headroom". How much headroom is enough depends on the program material, but typically ranges from 12 dB to 20 dB. Professional systems operate at reference/nominal levels 12 dB higher than this, so they must be capable of passing signals up to +20 dBu (7.75 volts rms or 22 volts pk-pk) without clipping to preserve 16 dB of headroom. The main difference between "pro" and "consumer" or "MI" (musical instrument) gear is the choice of interface. Unbalanced interfaces are suitable only for very short cables. Common-impedance coupling is inherent to unbalanced interfaces and is its downfall in high-performance audio systems. Only gear with balanced interfaces is worthy of the term "professional". However, modern "pro" interfaces based on simple diff-amps have tarnished the reputation of balanced interfaces unfairly - but that's another story - see http://www.jensentransformers.com/an/ingenaes.pdf for the how and why. Then you'll realize why the IEC changed the test procedure for "balanced inputs" back in 2000. --- Bill Whitlock, president and chief engineer, Jensen Transformers, Inc., AES Fellow and IEEE Senior Member.

Guru of Grounding
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re: Why Use a Better DAC?
Guru of Grounding   12/6/2008 11:23:55 PM
NO RATINGS
The author has confused the issue of differing level standards between professional and consumer audio equipment. First, the nominal or "reference level" signals are +4 dBu (1.23 volts rms) in pro gear and -10 dBV (0.316 volts rms) in consumer gear. The 2.0 volt rms or 5.6 volt pk-pk number for consumer gear refers to a full-scale rating. This level is only 16 dB higher than the consumer reference by the way, not 22 dB. Therefore, a consumer output is still legitimately rated at -10 dBV reference level but will clip at an output level 16 dB higher - this is referred to as "headroom". Professional systems operate at levels 12 dB higher than this, so they must be capable of passing signals up to +20 dBu (7.75 volts rms or 22 volts pk-pk) without clipping to preserve 16 dB of headroom. The main difference between "pro" and "consumer" or "MI" (musical instrument) gear is the choice of interface. Unbalanced interfaces are suitable only for very short cables. Common-impedance coupling is inherent to unbalanced interfaces and is its downfall in high-performance audio systems. Only gear with balanced interfaces is worthy of the term "professional". However, modern "pro" interfaces based on simple diff-amps have tarnished the reputation of balanced interfaces unfairly - but that's another story - see http://www.jensentransformers.com/an/ingenaes.pdf for the how and why. Then you'll realize why the IEC changed the test procedure for "balanced inputs" back in 2000. --- Bill Whitlock, president and chief engineer, Jensen Transformers, Inc., AES Fellow and IEEE Senior Member.



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As data rates begin to move beyond 25 Gbps channels, new problems arise. Getting to 50 Gbps channels might not be possible with the traditional NRZ (2-level) signaling. PAM4 lets data rates double with only a small increase in channel bandwidth by sending two bits per symbol. But, it brings new measurement and analysis problems. Signal integrity sage Ransom Stephens will explain how PAM4 differs from NRZ and what to expect in design, measurement, and signal analysis.

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